Absorption and disposition of drugs in patients are often different from those observed in normal volunteers. However, most of our current knowledge about drugs is obtained from studies of normal subjects. In this study we will determine the absorption and disposition of prednisone/prednisolone, quinidine, and cimetidine in the specific patient population where the use of these drugs has evidenced potential problems. Pharmacokinetic studies of prednisone/prednisolone will be carried out in renal transplant patients to elucidate the effect of food, antacids, and the cushingoid state on its bioavailability. Longitudinal studies will determine the relationships between pharmacokinetic parameters and cushingoid/non-cushingoid features. Studies of quinidine in renal and heart failure patients with arrhythmias will define the factors responsible for the observed wide variation in plasma concentrations of quinidine seen in patients. Pharmacokinetic studies of cimetidine will be carried out in hepatic alcoholic cirrhosis and hepatitis patients to establish the risk for central nervous system side effects in these patients. The studies outlined in the following proposal are designed to elucidate the absorption and disposition of prednisone/prednisolone, quinidine, and cimetidine in specific patient populations, and to establish a more judicial use of these drugs in patients.